The present invention relates generally to the field of robotics and to the field of intrusion detectors. More specifically, the present invention relates to the field of robotic intrusion detection systems.
One of the most promising applications for a mobile robotic system is that of a sentry or security guard, patrolling a designated area while monitoring for intrusion and other unwanted conditions such as fire, smoke and flooding. Technological barriers still exist, however, in the implementation of robotics that, in general, hinder near-term implementation of truly autonomous robotic systems. Most tasks performed by humans are extremely complex, requiring extensive hand-eye coordination skills as yet unreplicated by machines. To emulate even the most simplistic action involves acquiring large quantities of data describing the immediate environment, evaluating the data, and then effectuating some response. Current technology does not meet the needs for a reasonably adept and functional mobile system capable of performing human like tasks.
There are many benefits afforded by the utilization of robotic technology in a physical security and surveillance role. The advantage of a system that will not tire, become distracted, frightened, or even subversive are obvious and well-touted. Potential security functions assigned to such a system can be categorized into three general areas: (1) detection, (2) verification, and (3) assessment. Detection is readily addressable by a multitude of commercially available sensors. Verification involves cross checking with other sensors to lessen the chances of a false alarm and depends heavily upon both the type of detectors employed and the operating environment. While simultaneous utilization of a multitude of intrusion sensors has been proposed as in the "Denning Sentry" robot manufactured by Denning Mobile Robots of Woburn, Mass., no robotic intrusion alarm system to date includes the capability of verification through the utilization of cross checking with other sensors to lessen the chances of a false alarm. The assessment task acts upon the data collected to ascertain the nature of the disturbance, usually in order to determine if a response is necessary.
The type of intrusion sensors utilized in a security system are a function of a given application and include those specifically configured to detect intruders as well as those intended for detecting other unwanted conditions as described above. Intrusion is most easily recognized through the use of some type of motion detection scheme or sensor. Described below are several known intrusion sensors.
A very simple form of passive detection capability intended primarily for indoor scenarios is achieved by the utilization of a microphone which "listens" for sounds in the protected area. Vibration monitoring sensors may also be utilized and are usually coupled to the floor through wheel contact when deployed on a mobile platform.
An example of an optical motion detector which responds to changes in perceived light level is manufactured by Sprague, model number ULN-2232A. This integrated circuit incorporates a built-in lens to create a cone-shaped detection field. After a brief settling period upon power-up, the circuit adjusts itself to ambient conditions and any subsequent deviations from that set point result in an alarm output. The low cost and directional nature of the device allows for several to be used collectively in an array to establish unique detection zones which help locate the relative position of the suspected security violation. The ability to provide geometric resolution of the intruder's position can be invaluable in tailoring an appropriate response in minimal time.
Passive infrared motion detectors have recently been employed for intrusion detection. Originally designed for both indoor and outdoor fixed installation security systems, this type of pyroelectric sensor has been utilized on mobile robots due to its small size, low power consumption and excellent performance and reliability characteristics. The principle of operation of such a detector is essentially the same as that of the optical ULN-2232A sensor described above except that a different wavelength (10 micrometer) in the energy spectrum is sensed.
Microwave motion detectors may also be utilized for intrusion detection and operate at radio frequency. Such detectors rely on the Doppler shift introduced by a moving target to sense the relative motion of an intruder. The electromagnetic energy associated with such detectors can penetrate hollow walls and doorways thereby allowing the sensor to "see" into adjoining rooms in certain circumstances. This can be used to advantage by a robot patrolling a hallway to check locked office spaces and storerooms without the need for actual entry into such spaces and rooms.
Video systems may also be utilized as intrusion detectors and offer an even more sophisticated method of sensing intrusion in outdoor as well as indoor applications with the added benefits of excellent resolution in the precise angular location of the intruder. A surveillance camera can be used to digitize a scene for comparison with a previously stored image pattern representing the same region and significant deviations between the two can be attributed to motion within the field of view. "Windowing" techniques can be employed on most systems to selectively designate certain portions of the image to be ignored, such as a tree blowing in the wind, resulting in a significant reduction in nuisance alarm.
The traditional problem encountered in applying the aforementioned and other intrusion sensors in an automated security system has been the unacceptable increase in the nuisance alarm rate that occurs as the detector sensitivity is raised so as to provide the necessary high probability of detection. Operators quickly lose confidence in such systems where sensors are prone to false activation. As an example, passive infrared motion detectors can be falsely triggered by any occurrence which causes a localized and sudden change in ambient temperature within this sensor's coverage area. This can sometimes occur naturally as where a heating or cooling system is turned on or off. Optical motion detectors can be activated by any situation which causes a change in ambient light level. Again, this situation could be caused by some non-critical event, such as passing automobile headlights or lightning flashes. Discriminatory hearing sensors can be triggered by loud noises originating outside the protected area such as thunder, passing traffic or overflying aircraft. Microwave motion detectors can respond to rotating or vibrating equipment.